Recently, opportunities to use various services and contents through an information device with a wireless interface (communication device) such as mobile phones have been increasing. However, the wireless network used for such opportunities intrinsically does not provide stable quality, and bandwidth of the wireless network is generally narrow compared with a wired communication network. Therefore, currently such communication cannot always operate seamlessly.
Technologies have been developed to virtually increase bandwidth by using a plurality of peripheral wireless devices. For example, a plurality of routes via a plurality of terminals connected to a network by using Mobile IPv4 can be bundled, and packets in each path distributed and aggregated at a Home Agent (HA), thereby virtually increasing bandwidth. However, this method has high packet header overhead because it requires Internet Protocol (IP) tunneling by Mobile IP up to the HA where packets are distributed and aggregated at the upper stream of the public network, and further requires additional IP tunneling to transfer the packets to other wireless terminals nearby.
More specifically, when the wireless terminal in a local network transmits a packet to a Correspondent Node (CN) in a remote network via the other wireless terminal, there is a problem of superimposing encapsulation; that is, performing encapsulation for IP tunneling of Mobile IP and further performing encapsulation for IP tunneling to transfer packets from one wireless terminal to the other wireless terminal. In this case, the conventional method results in increased overhead of packet header information due to IP tunneling.
In order to solve these problems, a method to distribute and integrate routes by a VPN (Virtual Private Network) server has been proposed. The basic operating principle is explained by using an example of downstream route integration (from the CN to a wireless terminal MN).
FIG. 14 shows a conventional integration of a plurality of routes. In FIG. 14, packets from the CN (e.g., a file server 102) to a wireless terminal MN2 are transmitted by using three routes (directly/via the wireless terminal MN1/via a wireless terminal MN3). The wireless terminals MN1, MN2, and MN3 have two communication interfaces (such as a wireless LAN and the Cell Phone Network).
The file server 102 and a VPN server 101 connect to a remote network RN, and the wireless terminals MN1, MN2, and MN3 can be connected to the VPN server 101 via the Cell Phone Network. The wireless terminals MN1, MN2 and MN3 are connected to the file server 102 by way of the VPN server 101. Moreover, the wireless terminals MN1, MN2 and MN3 are connected to the file server 102 by using VPN connection. And, wireless terminals MN1, MN2 and MN3 are connected by using Wireless LAN LN.
That is, the VPN addresses are used in the wireless LAN LN and the remote network RN, and the global addresses are used between the VPN server 101 and the wireless terminals MN1 and MN2 (in the Internet).
Next, the transmission of the packets 1400-1, 1400-2, and 1400-3 from file server 102 to Wireless terminal MN2 will be explained.
First, the file server 102 sends packets 1400-1, 1400-2, and 1400-3 to VPN server 101. At this time, the file server 101 sets the VPN address of the wireless terminal MN2 to the destination address (Dst) of each packet 1400-1, 1400-2, and 1400-3.
The VPN server 101 encapsulates the packets 1400-1, 1400-2, and 1400-3 received from the file server 101. (encapsulated packets 1400-1, 1400-2, and 1400-3 correspond to packets 1400-(1), 1400-(2), and 1400-(3)).
At this time, the VPN server 102 sets the global address of the wireless terminal MN1 to the destination address (DST) of packet 1400-(1). And, the VPN server 102 sets the global address of the wireless terminal MN2 to the destination address (Dst) of packets 1400-(2) and sets the VPN address of the wireless terminal MN3 to the destination address (Dst) of packets 1400-(3).
Next, the VPN server 101 sends the encapsulated packets 1400-(1), 1400-(2), and 1400-(3) via the wireless LAN LN. After that, the wireless terminal MN1, MN2, and MN3 decapsulate the packets 1400-(1), 1400-(2) and 1400-(3) respectively.
At this time, because the destination addresses (Dst) of the decapsulated packets 1400-1, 1400-2, 1400-3 are the VPN address of the wireless terminal MN2, the wireless terminals MN1 and MN3 send the packets 1400-1 and 1400-2 to the wireless terminal MN2 by using Wireless LAN LN.
FIG. 15 shows an exemplary network configuration in which connection is made from a laptop computer in a local area network (LAN) to a remote network by way of a wireless terminal serving as a gateway (GW). In FIG. 15, when connection to the file server 102 is made from the laptop computer via the wireless terminal MN, the wireless terminal MN can be regarded as the GW from the LAN which includes the laptop PC to the external network. Since a private address is used in a local network, a Network Address Translation (NAT) function is required.
FIGS. 16 and 17 show exemplary routing controls when integration of a plurality of routes are applied to the configuration shown in FIG. 15.
First, an example of upper stream control is shown in FIG. 16 (from a laptop computer to file server 102).
In FIG. 16, a wireless terminal MN3 (such as the laptop computer) requests data transfer to the file server 102. At this time, a destination address Dst of the packet P10 is the address of the file server 102, and a transmission source address Src is a local (private) address of the wireless terminal MN3.
When the packet P10 passes through the wireless terminal MN1, the transmission source address Src of the packet P10 is translated to the VPN address of the wireless terminal MN1 by NAT (Network Address Translation) and the packet P10 turns into a packet P20. At this time, the address translation rule is stored in the wireless terminal MN1. Then the packet P20 is encapsulated at the wireless terminal MN1.
After encapsulation the packet P20 (packet P(20)) is transmitted from the wireless terminal MN1 to the VPN server. The VPN server 101 decapsulates the packet P (20). After that, the VPN server 101 sends the packet P20 (decapsulated from the packet P (20)) to the file server 102.
Now an example of downstream control (from file server 102 to the wireless terminal MN3) shown in FIG. 17 will be explained.
In this explanation, a destination address Dst of a packet P30 transferred from the file server 102 is the VPN address of the wireless terminal MN1. The packets P30-1 and P30-2 are encapsulated at the VPN server 101 so that the address after encapsulation includes the global addresses of the wireless terminals MN1 and MN2, respectively. The encapsulated packets are assumed to be P (30-1), and P (30-2), respectively. The packets P (30-1) and P (30-2) are transferred from the VPN server to the wireless terminal MN1 and MN2, respectively.
When the packet P (30-1) arrives at the wireless terminal MN1, it is decapsulated by the wireless terminal MN1, and a packet P30-1 is obtained. The packet P (30-2) at the wireless terminal MN2 is also decapsulated. The decapsulated packet P30-2 is transferred to the wireless terminal MN1 according to a predetermined routing setting. The packets P30-1 and P30-2 addressed to the VPN address of the wireless terminal MN1 and received at the wireless terminal MN1 are transferred to the wireless terminal MN3 as a packet P40, after translating the transmission source addresses Src into the address of the wireless terminal MN3 according to a stored address translation rule table T1.
However, each of the packets P (30-1) and P (30-2) are transferred to the wireless terminal MN3 always by way of the wireless terminal MN1 in order to apply address translation according to the address translation rule table T1. Therefore, the load to the wireless terminal MN1 increases and may cause delay in each process in the wireless terminal MN1 and increase power consumption as well.
The typical technology uses the wireless LAN network for one more hop compared with transferring packets directly from the wireless terminal MN2 to the wireless terminal MN3. This redundant transfer may reduce end-to-end throughput if terminals using the same channel increase.